1. Field of the Invention
The present invention relates to a data processing device, a program, an ink jet printing system and a data processing method which generates data for performing printing in different ink ejection volumes (ink dots in different sizes).
2. Description of the Related Art
In an ink jet printing device, there has been recently made an attempt for forming an image with a higher quality by making a size of a record droplet small. As one example of the ink jet printing device, there is known a printing device which applies ink of the same color with plural ejection volumes to carry out the printing, thus carrying out both of high-quality printing and high-speed printing.
Image data used in this ink jet printing device are acquired by finally converting image data in which the gradation sequence is expressed in the form of a multi-value (for example, 256 gradation sequence levels from 0 to 255 of 8 bits) for each pixel into binary image data. More specially, the image data of 256 values of 8 bits are once converted into N-value data (for example, four-value data) of plural bits (for example, two bits) expressing the gradation sequence of several levels. This conversion is called quantization. Based upon a level expressed by the quantized N-value data, a dot matrix pattern in advance addressed to the level is selected and binary image data for forming dots of the selected pattern are generated. The gradation sequence properties and the maximum density in printing can be set by appropriately defining the dot number and the dot arrangement in the dot matrix pattern. It should be noted that the dot matrix pattern means a dot arrangement pattern defining the arrangement of dots. Hereinafter, “dot matrix pattern” is also called “dot arrangement pattern”.
A concrete example of this method will be explained with reference to an example of a printing device which can record large, medium and small-sized dots. First, in regard to each of the large, medium and small-sized dots, the image data of 256 gradation sequence levels of 0 to 255 are quantized to four-value data (levels of 0 to 3) expressed in 2 bits. Next, the four-value data corresponding to each of the large, medium and small-sized dots are converted into 2-value data with the dot matrix pattern corresponding to any of levels of 0 to 3 shown in FIG. 12. As described above, this construction independently defines an arrangement of each of the large, medium and small-sized dots in regard to each level of the four levels (levels of 0 to 3). That is, the large, medium and small-sized data can be independently quantized. In the present specification, quantization data acquired by such an independent quantization (for example, index data showing each level for expressing the large, medium and small-sized dot data as shown in FIG. 12 as an independent pattern) are defined as a large, medium and small-size dot independent index. A method for independently generating data of dots in different sizes by using different dot matrix patterns respectively is disclosed by Japanese Patent Laid-Open No. 2004-148723 or Japanese Patent Laid-Open No. 2002-301815.
On the other hand, in the large, medium and small-size independent index, the large, medium and small-size dot data respectively are independently quantized, but the image data of a multi-value are quantized using the same matrix pattern, making it possible to generate dot data of the large, medium and small sizes. In a case of this construction, first, the image data of 256 gradation sequence levels from 0 to 255 corresponding to the same color are quantized to eight-value data (levels 0 to 7) expressed by 4 bits. Next, the eight-value data are converted into binary data by the dot matrix pattern (mixing pattern of large, medium and small-sized dots) corresponding to any of levels 0 to 7 as shown in FIG. 11. As described above, in this construction, the large, medium and small-size dot data are quantized together. In the present specification, quantization data acquired by such same quantization (for example, index data showing each level for expressing the large, medium and small-size dot data as shown in FIG. 11 as a mixing pattern) are defined as a large, medium and small-size dot same index. A method for generating data of dots in different sizes by using a single dot matrix pattern is disclosed by Japanese Patent Laid-Open No. 10-278244 (1998).
However, the large, medium and small-size same index and the large, medium and small-size independent index respectively have an advantage and a disadvantage in printing. FIG. 10 is a diagram summarizing the advantage and disadvantage of each. In addition, FIG. 11 is a diagram showing the dot matrix patterns by the large, medium and small-size same index and FIG. 12 is a diagram showing the dot matrix patterns by the large, medium and small-size independent index. Each dot matrix pattern is a dot matrix pattern of 2×2 in which one pixel has a size of 600 dpi (lateral)×600 dpi (vertical).
In the large, medium and small-size same index shown in FIG. 11, the same quantization processing is carried out for generating the large, medium and small-size dot data and the dot matrix pattern defines a position relation of the large, medium and small-sized dots in a pixel unit. Therefore, for example, in the connection section of the gradation sequence between a level where small-sized dots only are used (level 2 in FIG. 11) and a level where an medium-sized dot and a small-sized dot are mixed (level 3 in FIG. 11), an arrangement where the medium-sized dot and the small-sized dot are difficult to be overlapped can be defined. Likewise, in the connection section of the gradation sequence between a level where medium-sized dots only are used (level 4 in FIG. 11) and a level where an medium-sized dot and a large-sized dot are mixed (level 5 in FIG. 11), an arrangement where the medium-sized dot and the large-sized dot are difficult to be overlapped can be defined. In the dot pattern where the medium-sized dot and the small-sized dot are mixed or the medium-sized dot and the large-sized dot are mixed, when the dots are overlapped with each other, density of the dot is increased. Therefore, the dot is easy to be recognized in the record result, leading to an improvement on granular feelings. However, since in the large, medium and small-size same index, the arrangement where the medium-sized dot and the small-sized dot or the medium-sized dot and the large-sized dot are difficult to be overlapped can be defined, the granular feeling which may be the problem in a density region (gradation sequence level) where dots in different sizes start to be mixed can be reduced.
However, in a case of the large, medium and small-size same index, when an ejection volume of the medium-sized dot or the small-sized dot varies due to external factors to make almost no difference in ejection volumes between the medium-sized dot and the small-sized dot, the gradation sequence properties tends to be degraded. That is, when almost no difference in ejection volumes between the medium-sized dot and the small-sized dot is made, for example, a difference in an ink amount between level 2 and level 3 in FIG. 11 is made small. Since the dot arrangement of the medium-sized dot and the small-sized dot is defined in a pixel unit, the sufficient density is not produced in level 3 where the small-sized dot in level 2 is replaced by the medium-sized dot and the gradation sequence properties in the connection section of the gradation sequence between level 2 and level 3 tend to be degraded. The same problem may take place in the connection section of the gradation sequence from the medium-sized dot to the large-sized dot.
On the other hand, in the large, medium and small-size independent index shown in FIG. 12, the large, medium and small-sized dot data are independently quantized and the dot matrix pattern is defined to each of the large, medium and small-sized dots. Therefore, in the connection section of the gradation sequence from the small-sized dot to the medium-sized dot or in the connection section of the gradation sequence from the medium-sized dot to the large-sized dot, it can be freely determined from which level the input of the medium-sized dot or the large-sized dot starts to be made. In this case, even if an ejection volume of the medium-sized dot or the small-sized dot varies due to external factors, the gradation sequence properties are difficult to be degraded. This can be true of the connection section of the gradation sequence from the medium-sized dot to the large-sized dot.
However, in the large, medium and small-size independent index, the large, medium and small-sized dots are independently quantized and the dot matrix pattern is independently allotted to each of the large, medium and small-sized dots. Therefore, the position relation in a state where the large, medium and small-sized dots are mixed can not be defined. In consequence, when the gradation sequence where the small-sized dot only exists is shifted to the gradation sequence where the medium-sized dot and the small-sized dot are mixed, a portion where the medium-sized dot and the small-sized dot are overlapped is produced, so that start of the input of the medium-sized dot may stand out. When the gradation sequence where the medium-sized dot only exists is shifted to the gradation sequence where the medium-sized dot and the large-sized dot are mixed, the same phenomenon takes place.
As described above, the same index and the independent index respectively have the advantage and disadvantage. Therefore, in the conventional method of using only one of both, it is difficult to simultaneously achieve both of granular feeling reduction of the dot and gradation sequence properties in a density region (gradation sequence level) where the dot in a different size starts to enter in.